Field of the Invention
This invention relates to apparatus for a copy machine for determining whether the developer material in a container of the machine is at a predetermined level and in particular to such an apparatus which provides an electrical signal when there is an absence of the developer material at the predetermined level.
During operation of the copy machine the supply of developer material (liquid or powder) for the machine is normally out of view of the operator making it desirable that any apparatus provided to give an indication when the supply of developer material is not at a predetermined level be capable of providing such indication at a point where it can be readily seen by the operator. The remote indication can be easily provided when the apparatus provides an electrical signal which is initiated when the developer material recedes to a desired predetermined level. For example, an electrical signal can be used to control the operation of an indicating lamp located at a point within the view of operator. U.S. Pat. No. 3,593,842 to Richard C. Berg indicates that an attempt has been made to use a photocell toward which light is directed with the photocell being activated when the supply of developer material between the light source and the photocell is diminished. It is indicated that such an arrangement has been undesirable since the photocell may become coated with developer material and thus presents a condition where it will not be activated even when the entire supply of developer material has been used. Since the sensing portion of the photocell arrangement would be best located within the container for the developer material, periodic cleaning of the photocell arrangement is extremely difficult since containers for developer material are generally constructed in a manner where ready access to the interior of the container is not provided.